There is a conventional technique of detecting a target object in an image using two detectors different in performance. This technique reduces the number of false positives that may occur when a detector storing data obtained by previous learning cannot completely be adapted to the circumstances of its installed place. In the technique, first detection is performed to detect a target object in the whole image, using a first detector, and then second detection is performed on the first detection result, using a second detector. By setting, as a detection result, the object detected by both detectors, detection of an object that should not be detected is suppressed.